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Advice diagnosing large muzzle velocity spreads

Looking for advice diagnosing large muzzle velocity spreads. This is the second powder test as the video camera failed to record shots on target on a previous test. From velocities on that previous test I was favouring 43.2. Therefore I loaded 6 sighters at 43.2. Again 43.2 looked like the spot.

BUT look at the 77 fps spread of the 7 shots at 43.2. (6 sighters and 1 in ladder) I haven’t been able to trim down my ES after months of refining. Different brass, primers, bullets(Sierra,Berger,Hornady) weights, techniques, etc.

I will list details of this test in case it may help someone spot any issues:

Tikka varmint 308, 24” barrel, 1-11 twist, bedded into MDT chassis.

Lapua brass, Varget, 175 TMK, CCI BR2.

Brass is annealed, FL sized with Redding S type with no bushing .002 bump, neck sized with Lee collet using torque wrench at 35 foot lbs. Trimmed, chamfered, brushed.

Powder is measured with a tuned RCBS 502 with camera that is proven repeatable and sensitive to one kernel of Varget.

Bullets seated with Forster micrometer die.

I don’t know where to go from here.

Thanks in advance.
 

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Looking for advice diagnosing large muzzle velocity spreads. This is the second powder test as the video camera failed to record shots on target on a previous test. From velocities on that previous test I was favouring 43.2. Therefore I loaded 6 sighters at 43.2. Again 43.2 looked like the spot.

BUT look at the 77 fps spread of the 7 shots at 43.2. (6 sighters and 1 in ladder) I haven’t been able to trim down my ES after months of refining. Different brass, primers, bullets(Sierra,Berger,Hornady) weights, techniques, etc.

I will list details of this test in case it may help someone spot any issues:

Tikka varmint 308, 24” barrel, 1-11 twist, bedded into MDT chassis.

Lapua brass, Varget, 175 TMK, CCI BR2.

Brass is annealed, FL sized with Redding S type with no bushing .002 bump, neck sized with Lee collet using torque wrench at 35 foot lbs. Trimmed, chamfered, brushed.

Powder is measured with a tuned RCBS 502 with camera that is proven repeatable and sensitive to one grain of Varget.

Bullets seated with Forster micrometer die.

I don’t know where to go from here.

Thanks in advance.

Frankly, I'd say it's mostly an issue with your scale. It looks like you're doing everything else well, but the scale is letting you down. I say this because I had used my RCBS balance beam scale in the same way as you and likewise could see sensitively to one gradual of Varget. And like you, it wasn't unusual to see ES's in in the 70's and occasionally in the 80's. Sometimes I could get ES's in the 30's, but not really consistently. So I bought a ChargeMaster 1500 and my ES's dropped into the 20's & 30's pretty consistently (some variance depending on the particular powder I was using). My goal was to get my SD's into the single digits and the ChargeMaster just wasn't doing it. So, I bit the bullet and got an FX-120i and wallah, single digits became consistent and ES's consistently in the teens; much of the time in the low teens depending on the primer I use.

IMHO, if you can't get low ES's and SD's, it's pointless to try to do a latter and it's better to just go by how the load is grouping (assuming the shooter is using good shooting mechanics).
 
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BUT look at the 77 fps spread of the 7 shots at 43.2. (6 sighters and 1 in ladder) I haven’t been able to trim down my ES after months of refining. Different brass, primers, bullets(Sierra,Berger,Hornady) weights, techniques, etc.
Tell us about the shot that measured 2591 fps.
Was it the first shot out of a cold clean barrel? Or was it somewhere else in the string. iI that 2591 shot was the first one, THROW OUT THAT NUMBER. IT IS AN EXPECTED ANNOMOLY
If it was, did you prep your barrel with something like Lock-Eez after cleaning?

Most cold clean barrel shots will have a slower velocity than the rest of the string. And, it may even shootin a different place.
If you throw out that 1 shot, the other 6 have an ES of 24 fps, not bad.
i
 
Tell us about the shot that measured 2591 fps.
Was it the first shot out of a cold clean barrel? Or was it somewhere else in the string. iI that 2591 shot was the first one, THROW OUT THAT NUMBER. IT IS AN EXPECTED ANNOMOLY
If it was, did you prep your barrel with something like Lock-Eez after cleaning?

Most cold clean barrel shots will have a slower velocity than the rest of the string. And, it may even shootin a different place.
If you throw out that 1 shot, the other 6 have an ES of 24 fps, not bad.
i

:eek: Yeah, it really helps to throw out those anomalies. ;) :p
 
Frankly, I'd say it's mostly an issue with your scale. It looks like you're doing everything else well, but the scale is letting you down. I say this because I had used my RCBS balance beam scale in the same way as you and likewise could see sensitively to one grain of Varget. And like you, it wasn't unusual to see ES's in in the 70's and occasionally in the 80's. Sometimes I could get ES's in the 30's, but not really consistently. So I bought a ChargeMaster 1500 and my ES's dropped into the 20's & 30's pretty consistently (some variance depending on the particular powder I was using). My goal was to get my SD's into the single digits and the ChargeMaster just wasn't doing it. So, I bit the bullet and got an FX-120i and wallah, single digits became consistent and ES's consistently in the teens; much of the time in the low teens depending on the primer I use.

IMHO, if you can't get low ES's and SD's, it's pointless to try to do a latter and it's better to just go by how the load is grouping (assuming the shooter is using good shooting mechanics).
Thanks for the reply. I'm thinking you are probably correct. I'm not sure what else it could be. Neck tension should be fairly consistent. I've tested that scale and it checked out but I've been doubting it. Yeah
 
Tell us about the shot that measured 2591 fps.
Was it the first shot out of a cold clean barrel? Or was it somewhere else in the string. iI that 2591 shot was the first one, THROW OUT THAT NUMBER. IT IS AN EXPECTED ANNOMOLY
If it was, did you prep your barrel with something like Lock-Eez after cleaning?

Most cold clean barrel shots will have a slower velocity than the rest of the string. And, it may even shootin a different place.
If you throw out that 1 shot, the other 6 have an ES of 24 fps, not bad.
i
Thanks for the reply. 2591 was not the first shot of the day. As I was trying a new scope I had fired maybe 6 shots of Federal GM/168 Sierras to zero the scope. There was a fair bit of time between then and starting the test. So warm but not hot. Barrel was cleaned the night before with KG-1 carbon remover and Bore Tech Eliminator, nylon brush, patched, nothing else.
 
Although in theory the bullet will leave the barrel before recoil can affect it I tend to think otherwise. These two groups were shot at 300 yards with ammo loaded that was loaded in same sitting and randomly pulled from the ammo box. The barrel was cooled for 15 min between strings. The only difference in the shooting would be that I removed my jean jacket and was only wearing a heavy sweatshirt on the right hand group. Temp was 55° , sunny and barrel was allowed to cool for 15 min between strings. I shifted my scope 1.5 MOA to the right for the second group and used the left hand dot for the aim point. Major difference in velocity numbers and group size
 

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Although in theory the bullet will leave the barrel before recoil can affect it I tend to think otherwise. These two groups were shot at 300 yards with ammo loaded that was loaded in same sitting and randomly pulled from the ammo box. The barrel was cooled for 15 min between strings. The only difference in the shooting would be that I removed my jean jacket and was only wearing a heavy sweatshirt on the right hand group. Temp was 55° , sunny and barrel was allowed to cool for 15 min between strings. I shifted my scope 1.5 MOA to the right for the second group and used the left hand dot for the aim point. Major difference in velocity numbers and group size
I never considered that technique might affect ES. Thanks Jim!
 
The velocities for shots 1-8 exhibit a clear increasing trend; like the scale is drifting, barrel heating, etc. What else?

To assess the scale you could weigh out 10 charges as normal, then reweigh them to assess for uniformity or a trend.
I may have misunderstood you but shots 1 thru 10 each have an increased powder weight of .3 grains. That would account for the increasing trend in velocities. The 7 shots all at 43.2 grains ( 6 sighters and shot #6 in the test) are an example showing the inconsistencies I've been seeing.
 
Forget the ES of a ladder test ( it is suppose to have increases) and re shoot 8-9-10 using 3 of each charge
 
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I'm making the assumption that the 2591 fps value was the fist shot out of a clean bore. If so, then you're really only looking at an ES from 2644 to 2668, or 24 fps for 6 shots. Not outstanding, but likely far better than a typical commercial ammunition prep.

As mentioned by jr600yd above, have you considered testing different primers?

Additionally, you might consider checking your charge weights using a different scale. For example, the Gem20 would be a relatively inexpensive option that could be used to test/compare the charge weights thrown from your RCBS 502 beam balance. The Gem20 is a nice little balance (reviewed here: https://forum.accurateshooter.com/threads/remarkable-little-scale.3985753/#post-37565156) that will set you back around $40.00 (they were only about $20.00 one year ago). You mentioned in the original post that your RCBS 502 is "proven repeatable and sensitive to one grain of Varget." I'm hoping that was a typo and you meant "0.1 gr Varget". One full gr of Varget could be worth anywhere from 50-75 fps solely in terms of increasing charge weight. In terms of ES, that relatively low level of precision in powder delivery could wreak havoc with your ES/SD values.

Other possible ways to minimize ES/SD would include sorting cases by volume or weight, and paying special attention to case neck tension (interference fit). It might also be worth a try to test different neck tensions (i.e. use different size bushings and/or mandrels to size some brass) and determine whether there is any effect on ES/SD. An approach such as that only need be done with as many pieces as you need for the test, let's say at least 5 pcs. per neck tension, rather than a large number of cases.
 
What was your bullet seating depth or how far off the lands were you is a better question ? Bro. These bullets normally like about .020 jump in my rifle. This was loaded with your same components except I was only loading 43.0 gr. of Varget.
 

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Straightshooter1
I'm making the assumption that the 2591 fps value was the fist shot out of a clean bore. If so, then you're really only looking at an ES from 2644 to 2668, or 24 fps for 6 shots. Not outstanding, but likely far better than a typical commercial ammunition prep.
2591 was around the 7th shot. I fired approx 6 zeroing in a changed out scope before the test.
As mentioned by jr600yd above, have you considered testing different primers?
Yes I've tried Federal 210m. Didn't see anything different.
Additionally, you might consider checking your charge weights using a different scale. For example, the Gem20 would be a relatively inexpensive option that could be used to test/compare the charge weights thrown from your RCBS 502 beam balance. The Gem20 is a nice little balance (reviewed here: https://forum.accurateshooter.com/threads/remarkable-little-scale.3985753/#post-37565156) that will set you back around $40.00 (they were only about $20.00 one year ago). You mentioned in the original post that your RCBS 502 is "proven repeatable and sensitive to one grain of Varget." I'm hoping that was a typo and you meant "0.1 gr Varget". One full gr of Varget could be worth anywhere from 50-75 fps solely in terms of increasing charge weight. In terms of ES, that relatively low level of precision in powder delivery could wreak havoc with your ES/SD values.
I meant sensitive to 1 kernel of Varget. That said, yes I'm starting to think you and Straightshooter1 are correct about the scale. I think I'll focus on that first.
Other possible ways to minimize ES/SD would include sorting cases by volume or weight, and paying special attention to case neck tension (interference fit). It might also be worth a try to test different neck tensions (i.e. use different size bushings and/or mandrels to size some brass) and determine whether there is any effect on ES/SD. An approach such as that only need be done with as many pieces as you need for the test, let's say at least 5 pcs. per neck tension, rather than a large number of cases.
Thanks Ned
 
What was your bullet seating depth or how far off the lands were you is a better question ? Bro. These bullets normally like about .020 jump in my rifle.
Short story: .151 off lands. (2.87 coal) for this particular test
Long story: Previously I was hand feeding rounds and I would start seating tests at .014 off lands and work farther in .003 increments with 3 round groups. Rifle seemed to like .034 off lands wth this bullet.
This test though was to develop a load that would fit in my magazine so I am loading them at .151 off lands. (2.87 coal). I will now run another test moving back from there in .003 increments to find a sweet spot.

That said it's the large velocity spreads that I'm getting through different loads that I'm hoping to resolve. The above is just a recent test that I am using a portion of it to show an example of that, not the test as a whole.

Thanks Bill
 
Forget the ES of a ladder test ( it is suppose to have increases) and re shoot 8-9-10 using 3 of each charge
Sorry I may have made a mistake using the above test as an example. Basically ignore the test as a whole as to the question at hand :-)
The 7 shots all at 43.2 grains ( 6 sighters and shot #6 in the test) are what I wanted to show as an example showing the ES inconsistencies I've been getting for many months of trying to refine my loading process.

Thanks SPJ
 
Short story: .151 off lands. (2.87 coal) for this particular test
Long story: Previously I was hand feeding rounds and I would start seating tests at .014 off lands and work farther in .003 increments with 3 round groups. Rifle seemed to like .034 off lands wth this bullet.
This test though was to develop a load that would fit in my magazine so I am loading them at .151 off lands. (2.87 coal). I will now run another test moving back from there in .003 increments to find a sweet spot.

That said it's the large velocity spreads that I'm getting through different loads that I'm hoping to resolve. The above is just a recent test that I am using a portion of it to show an example of that, not the test as a whole.

Thanks Bill

On running your numbers with the 175 TMK's through my QuickLoad app it makes me wonder if some of you're issue is with a compressed load since QL shows case fill to be 103% of case capacity??? Anyway . . . here's what I'm looking at and thought you might like to see too:

QL.jpg
 

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